My back round is in transportation and the answer is fairly simple. If you use your vehicle, whether it’s a ½ ton, ¾ ton, 1ton and bigger, to transport goods or services that generate you an income, you are subject to the DOT laws that apply to the weight classification of your truck and trailer. This also requires a DOT number on the side of your vehicle. This applies to lawn care businesses, electrician’s, plumbers and contractors.
If you use that exact same vehicle for your own personal use, you are not required to have a DOT number, stop at any scales or follow any DOT regulations. Your vehicle still must be legal, with working lights, brakes, safety chains….etc.
Hope this helps you decide if you need a DOT number or not.